I’ve noticed something similar on my instance in some cases as well. Nothing obvious logged as errors either. It just seems like the comment was never sent. In my case cpu is minimal so it doesn’t seem like a resource issue on the receiving side.
I suspect it may be a resource issue on the sending side. Potentially, not able to keep up with the number of subscribers. I know there was some discussion from the devs around the number of federation workers needing to be increased to keep up, so another possibility there.
It’s definitely problematic though. I was contemplating implementing some kind of resync this entire post and all comments via the Lemmy API to get things back in sync. But, if it is a sending server resource issue, I’m also hesitant to add a bunch more API calls to the mix. I think some kind of resync functionality will be necessary in the end.
I also just recently switched to https://purelymail.com after hosting my own for several years via Mailcow and a cheap VPS. The cheap VPS was more expensive than the $10/year for Purelymail and I was only using it for mail anyway. Nothing to maintain now and so far very happy with how easy it was to move everything over.
Also, they don’t charge extra for additional domains so if you have multiple it’s still $10. Only been with them a few weeks so can’t say much yet for long term, but great so far!